Looks like your parts have been anodized. You'll have to remove that first. Good lye solution should do it. Easy Off will. Achieving the finish, shiny or not is just the right combo of compounds/sanding/lube/scrubbies in whatever combination you choose. You can even polish that with Old Dutch or Ajax or whatever. Just practice somewhere on a scrap piece.
Keeping it in good shape once done and no anodizing left you'll be cleaning poolishing a lot more, shiny or not. They don't anodize them soft alloys just for looks.Soft alloys they have to seal the pores otherwise crud/salt gets in there and you won't get rid of it easily. I am not into the shiny looks but it sure is easier to maintain, crud & salts don't get in the pores so much and it depends a lot also on the type of alloys used.
Lets say that I have polished way too much Aluminium kitchen equipment and motorcycle parts in 30+ years to care much about doing that anymore. Mostly done with stuff from under the kitchen sink or when I am at sea.....cleaning locker.
Powdercoating? I just bought the 1200 degree powder in "Brushed Aluminium" color, haven't tried it yet. Will be doing some tests this week maybe.